Introduce o3tl::optional as an alias for std::optional

...with a boost::optional fallback for Xcode < 10 (as std::optional is only
available starting with Xcode 10 according to
<https://en.cppreference.com/w/cpp/compiler_support>, and our baseline for iOS
and macOS is still Xcode 9.3 according to README.md).  And mechanically rewrite
all code to use o3tl::optional instead of boost::optional.

One immediate benefit is that disabling -Wmaybe-uninitialized for GCC as per
fed7c3deb3f4ec81f78967c2d7f3c4554398cb9d "Slience bogus
-Werror=maybe-uninitialized" should no longer be necessary (and whose check
happened to no longer trigger for GCC 10 trunk, even though that compiler would
still emit bogus -Wmaybe-uninitialized for uses of boost::optional under
--enable-optimized, which made me ponder whether this switch from
boost::optional to std::optional would be a useful thing to do; I keep that
configure.ac check for now, though, and will only remove it in a follow up
commit).

Another longer-term benefit is that the code is now already in good shape for an
eventual switch to std::optional (a switch we would have done anyway once we no
longer need to support Xcode < 10).

Only desktop/qa/desktop_lib/test_desktop_lib.cxx heavily uses
boost::property_tree::ptree::get_child_optional returning boost::optional, so
let it keep using boost::optional for now.

After a number of preceding commits have paved the way for this change, this
commit is completely mechanical, done with

> git ls-files -z | grep -vz -e '^bin/find-unneeded-includes$' -e '^configure.ac$' -e '^desktop/qa/desktop_lib/test_desktop_lib.cxx$' -e '^dictionaries$' -e '^external/' -e '^helpcontent2$' -e '^include/IwyuFilter_include.yaml$' -e '^sc/IwyuFilter_sc.yaml$' -e '^solenv/gdb/boost/optional.py$' -e '^solenv/vs/LibreOffice.natvis$' -e '^translations$' -e '\.svg$' | xargs -0 sed -i -E -e 's|\<boost(/optional)?/optional\.hpp\>|o3tl/optional.hxx|g' -e 's/\<boost(\s*)::(\s*)(make_)?optional\>/o3tl\1::\2\3optional/g' -e 's/\<boost(\s*)::(\s*)none\>/o3tl\1::\2nullopt/g'

(before committing include/o3tl/optional.hxx, and relying on some GNU features).
It excludes some files where mention of boost::optional et al should apparently
not be changed (and the sub-repo directory stubs).  It turned out that all uses
of boost::none across the code base were in combination with boost::optional, so
had all to be rewritten as o3tl::nullopt.

Change-Id: Ibfd9f4b3d5a8aee6e6eed310b988c4e5ffd8b11b
Reviewed-on: https://gerrit.libreoffice.org/84128
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 5 insertions, 5 deletions

diff --git a/unotools/inc/pch/precompiled_utl.hxx b/unotools/inc/pch/precompiled_utl.hxx
index ddffb5294b2b..7a2b9b826f49 100644
--- a/unotools/inc/pch/precompiled_utl.hxx
+++ b/unotools/inc/pch/precompiled_utl.hxx
@@ -32,7 +32,7 @@
 #include <vector>
 #include <boost/locale.hpp>
 #include <boost/locale/gnu_gettext.hpp>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 #endif // PCH_LEVEL >= 1
 #if PCH_LEVEL >= 2
 #include <osl/detail/file.h>
diff --git a/unotools/source/config/historyoptions.cxx b/unotools/source/config/historyoptions.cxx
index 164731398716..e65a2a98171b 100644
--- a/unotools/source/config/historyoptions.cxx
+++ b/unotools/source/config/historyoptions.cxx
@@ -34,7 +34,7 @@
 #include <comphelper/configurationhelper.hxx>
 #include <comphelper/processfactory.hxx>
 #include <tools/diagnose_ex.h>
-#include <boost/optional.hpp>
+#include <o3tl/optional.hxx>
 
 using namespace ::std;
 using namespace ::utl;
@@ -78,7 +78,7 @@ public:
 
     void AppendItem(EHistoryType eHistory,
         const OUString& sURL, const OUString& sFilter, const OUString& sTitle,
-        const boost::optional<OUString>& sThumbnail);
+        const o3tl::optional<OUString>& sThumbnail);
 
     void DeleteItem(EHistoryType eHistory, const OUString& sURL);
 
@@ -317,7 +317,7 @@ Sequence< Sequence<PropertyValue> > SvtHistoryOptions_Impl::GetList(EHistoryType
 
 void SvtHistoryOptions_Impl::AppendItem(EHistoryType eHistory,
         const OUString& sURL, const OUString& sFilter, const OUString& sTitle,
-        const boost::optional<OUString>& sThumbnail)
+        const o3tl::optional<OUString>& sThumbnail)
 {
     uno::Reference<container::XNameAccess> xListAccess(GetListAccess(eHistory));
     if (!xListAccess.is())
@@ -551,7 +551,7 @@ Sequence< Sequence< PropertyValue > > SvtHistoryOptions::GetList( EHistoryType e
 
 void SvtHistoryOptions::AppendItem(EHistoryType eHistory,
         const OUString& sURL, const OUString& sFilter, const OUString& sTitle,
-        const boost::optional<OUString>& sThumbnail)
+        const o3tl::optional<OUString>& sThumbnail)
 {
     MutexGuard aGuard(theHistoryOptionsMutex::get());